The invention relates to a halogen-free, flame-retardant thermoplastic polyester or polyamide composition that contains a combination of organic phosphorus compound and a nitrogen-containing flame retardant.
Such a composition is known from EP-A-672,717. This describes a flame-retardant polybutylene terephthalate, PBT, composition in which the organic phosphorus compound is a hydroquinone type of aromatic oligo- or polyphosphate and the nitrogen-containing flame retardant is a salt of a triazine derivative with at least one acid of cyanuric acid or isocyanuric acid. In the examples melamine, benzoguanamine and acetoguanamine are used as the triazine derivative. To obtain a UL-94 V-O classification, the compositions contain approx. 20 parts by weight of organic phosphorus compound and at least 8 parts by weight of triazine derivative per 100 parts by weight of PBT. With glass fibre present in the composition the required concentration of flame retardant combination was at least approx. 40 parts by weight per 100 parts by weight of PBT with 30 parts by weight of glass fibre.
Such high concentrations of flame retardant combination have a highly adverse influence on the polymer composition""s mechanical and processing properties. For example, a value of at least 50xc2x0 C. was found for the difference between Tm and Tc, Tm=melting point and Tc=crystallisation temperature, measured with differential scanning calorimetry (DSC), for the PBT-based compositions according to the aforementioned state of the art. For PBT without a flame retardant this difference is 35-40xc2x0 C. resulting in a shorter cycle time in injection moulding. It is also known that organic phosphorus flame retardants, which are fluid at room temperature, have an adverse effect on the polymer composition""s stiffness.
The invention""s object is hence a halogen-free flame-retardant thermoplastic polyester or polyamide composition that does not present the aforementioned drawbacks, or possesses them to a substantially lesser extent.
The invention""s object is achieved with a flame retardant combination that is characterised in that the compound derived from triazine is a melamine condensation product, preferably melam or melem. The invention also covers a halogen-free glassfibre reinforced thermoplastic polyamide composition in which the flame retardant combination is characterised in that the organic phosphorus compound contains at least 14 wt. % phosphorus and the compound derived from triazine is melamine cyanurate.
In principle, all the current thermoplastic polyesters and copolyesters and polyamides can be used as the thermoplastic polyester or polyamide for the composition. Examples of this are polyalkylene terephthalates or copolyesters thereof with isophthalic acid, for example polyethylene terephthalate, PET, polybutylene terephthalate, PBT, polyalkylene naphthalates, for example polyethylene naphthalate, PEN, polypropylene naphthalate, polybutylene naphthalate, PBN, polyalkylene dibenzoates, for example polyethylene dibenzoate and copolyesters hereof. Preferable are PET, PBT, PEN and PBN. Also suitable are block copolyesters which, in addition to hard polyester segments from the above group of thermoplastic polyesters, also contain soft polyester segments derived from at least one polyether or aliphatic polyester. Examples of such block copolyesters with elastomeric properties are for example described in xe2x80x9cEncyclopedia of Polymer Science and Engineeringxe2x80x9d, Vol. 12, p.75 ff. (1988), John Wiley and Sons and xe2x80x9cThermoplastic Elastomersxe2x80x9d, 2nd Ed., chapter 8 (1996) Hauser Verlag and the references mentioned therein.
Polyamides usefull in the practice of this invention include those which are well-known in the art, and for instance described in Encyclopedia op Polymer Science and Technology, Vol. 11, p.315, (1988) ISBN 0-471-80943-8 (V.11). The invention is especially very effective in polyamides having a melting point of higher than 265xc2x0 C. For instance polyamide 4.6 and the copolyamides based on aliphatic and aromatic dicarboxylic acids. Examples thereof are polyamide 6/6.T, 6.6/6.T, 6.6/6/6.T, 6.6/6.I/6.T etc.
Melamine condensation products are for example melam, melem, melon and menthone and can for example be obtained with the process described in WO-A-96/16948. Preferably the dimer, melam, or the trimer, melem, is used.
In the combination with a melamine condensation product the phosphorus compound can be chosen from the wide group of organic phosphates, phosphites, phosphonates and phosphinates. Preferably use is made of phosphates and phosphonates. Examples of such compounds are described in for example Kirk Othmer, Encyclopedia of chemical technology, Vol. 10, p.396 ff. (1980).
A large number is commercially available, for example resorcinolbis(diphenylphosphate) oligomer, under the trade name Fyrolflex RDP from AKZO-Nobel, NL; cresyldiphenylphosphate, CDP, under the trade name Kronitex CDP from FMC, UK; trimethylolpropanol ester of methyl phosphoric acid, under the trade name Amgard P45 from Albright and Wilson, USA; polypentaerythritol phosphonate under the trade name Cyagard RF 1041 from American Cyanamid, USA. Hostaflam OP 910; a mixture of cyclic di- and triphosphonates containing 21 wt. % P, from Hoechst, Germany.
It is particularly advantageous to use an organic phosphorus compound with a phosphorus content of at least 14 wt. %; preferably 18 wt. %. An example of this are Amgard P45, and the metal phosphinates as for instance in U.S. Pat. No. 4,208,321 and U.S. Pat. No. 3,594,347.
A practical requirement for the organic phosphorus compound is a low volatility at the processing temperatures of the polyester or polyamide composition and the service temperature of objects obtained from the composition. For this reason cresyldiphenylphosphate, for example, is less suitable for guaranteeing flame-retardant behaviour in the longer term.
The compositions of the invention can be obtained in a simple way by means of mixing in the melt. Use is then preferably made of an extruder fitted with means that make it possible to dose the phosphorus compound, which is usually fluid at room temperature already. It is also advantageous if fibrous reinforcing materials can be dosed to the melt separately. It is also possible that the flame retardant components are already present in the polymerisation process for the production of the polyamide or polyester.
The concentration of organic phosphorus compound may vary within a wide range, for example between 0.5 and 20 wt. %, preferably between 1 and 12 wt. %, even more preferably between 2 and 10 wt. %. The concentration of the compound derived from triazine may vary within a wide range, for example between 2 and 25 wt. %, preferably between 3 and 20 wt. %, most preferably between 4 and 16 wt. %. Weight percentages are relative to the composition""s total weight. A person skilled in the art will be able to determine the optimum composition in his case through systematic research.
The compositions according to the invention may furthermore contain the usual additives, for example heat stabiliser, UV stabilisers, pigments, processing agents, for example mould release agents, and fillers, for example clay and reinforcing fibres, for example glass fibres. More substances that improve the flame-retardant behaviour may optionally be added, for example char-forming substances such as polyphenylene ether and polycarbonate and substances that have an effect on the dripping behaviour, for example fluoropolymers such as polytetrafluoroethylene. Well-known stabilisers are for example hindered phenols.
In the presence of glass fibre reinforcement in particular the compositions according to the invention show surprising advantages. For example, the CTI, comparative tracking index, increases from approx. 350 Volt to 600 Volt, which presents particular advantages in electrical applications. In addition, moduli of elasticity are realized that have never before been published for polyester and polyamide compositions based on organic phosphorus-containing flame retardants with comparable flame-retardant behaviour.